Mindfulness-based interventions, an evidence-based stress reduction approach, may help incarcerated people cope with stress-related problems in the challenging environment of prison. However, due to their unique living environment, the duration and instructor guidance required by standard mindfulness-based interventions would be infeasible in most prisons. Therefore, the aims of the current study were to test the effects of two different 4-day interventions (i.e., instructor-guided and audio-based) with content similar to Mindfulness-Based Cognitive Therapy for newly incarcerated males, and to compare the effectiveness of the two interventions relative to a no-intervention control group. Using daily assessments, we explored changes in perceived stress, insomnia, and negative affect in the 56 days following the instructor-guided (N = 25), audio-based (N = 21), and control (N = 44) intervention; length of mindfulness practice during the follow-up was also compared between the two intervention groups. Hierarchical linear model results showed significantly greater linear decreases in perceived stress after both mindfulness interventions during the 56-day follow-up (γ11 = -0.011, p < .001, 95% CI [-0.017, -0.004] for instructor-guided intervention; γ12 = -0.013, p < .001, 95% CI [-0.018, -0.006] for audio-based intervention), as compared to the control group. Compared to the control group, the instructor-guided group reported a significantly greater decrease in insomnia (γ11 = -0.007, p < .001, 95% CI [-0.014, -0.002]), but the audio-based group did not (γ12 = -0.002, p = .160, 95% CI [-.007, .004]). Neither mindfulness-based intervention group reported a significantly greater decrease in negative affect compared to the control group (γ11 = -0.002, p = .170, 95% CI [-0.005, 0.001] for instructor-guided intervention; γ12 = -0.002, p = .150, 95% CI [-0.006, 0.002] for audio-based intervention). No significant difference between the two intervention groups was found in the change of outcomes (γ11 = 0.002, -0.005 and 0.000, p = .350, .130 and .390, 95% CI [-0.008, 0.011], 95% CI [-0.014, 0.004] and 95% CI [-0.004, 0.006] subsequently for perceived stress, insomnia and negative affect). Daily mindfulness practice was significantly longer for the audio-based group on the first day of follow-up (γ02 = -0.758, p < .05, 95% CI [-1.333, -0.129]), but it gradually decreased to the same amount as the instructor-guided group (t (32) = 0.051, p = .959). Short-term mindfulness interventions, either instructor-guided or audio-based, appear to be beneficial for Chinese prisoners in reducing stress. Live instruction may have potential benefit in reducing insomnia and sustaining daily practice.